The present communication gives an account of the isolation, structure and pharmacological properties of the caerulein-like polypeptide occurring in the skin of Phyllomedusa sauvagei from north-western regions of Argentina. For the new polypeptide, a nonapeptide closely resembling caerulein both from a biological and chemical point of view, the name phyllocaerulein is proposed. This paper also describes the occurrence of phyllocaerulein or related peptides in the skin of other Phyllomedusa species. A complete description of methods used in the isolation of phyllocaerulein as well as in the determination of amino-acid composition and amino-acid sequence of the polypeptide may be found in a preceding paper dealing with the isolation and the amino acid sequence of caerulein (Anastasi, Erspamer & Endean, 1968 ; Anastasi, 1969).Material digitalizado en SEDICI gracias a la colaboración del Dr. Jorge Williams (FCNM-UNLP).Facultad de Ciencias Naturales y Museo